Chemistry Reference
In-Depth Information
They are unstable at these temperatures and cannot be melt spun. Fibers, however, were prepared by
dry spinning from hydrocarbon suspensions [
49
]. Later, it was found that when the anionic ring
opening polymerizations of 2-pyrrolidone are activated by CO
2
in place of the
-acyl derivative, the
resultant higher molecular weight product has much better heat resistance [
54
]. This “new” nylon 4,
reportedly, can be melt spun.
Nylon 5
or poly(
N
-piperidone) can be prepared by ring opening anionic polymerization of valerolactam
[
53
]. The reaction requires very pure monomer to yield a high molecular weight polymer [
53
]:
a
H
H
N
n
N
O
n
O
One route to valerolactam is from cyclopentadiene:
[H]
[O]
O
Bechmann
rearrangement
H
2
NOH
O
OH
N
N
259
o
C
H
2
SO
H
Valerolactam can also be polymerized with the aid of coordination catalysts to a high molecular
weight polymer using alkali metal-Al(C
2
H
5
)
3
catalysts or alkali metal alkyl-Al(C
2
H
5
)
3
catalysts [
55
].
The polymerizations require
relatively long times
.
Nylon 6
is obtained via ring opening polymerization of caprolactam:
O
n
O
N
N
H
n
H
This polymer developed over the years into an important commercial material. As a result, many
preparatory routes were developed for the starting material and the polymerization reaction was
studied thoroughly.
The most common starting materials for preparations of caprolactam are phenol, cyclohexane, and
toluene. Some caprolactam is also made from aniline. In these synthetic processes, the key material is
cyclohexanone oxime. The route based on phenol can be shown as follows:
[H]
[O]
OH
OH
O
Beckmann
rearrangem
ent
H
2
NOH
O
NOH
250
o
C
H
2
SO
4
N
H
